1. Field of Invention
The present invention relates to projectors having a display feature in a wide color gamut, and more specifically, it relates to a projector which produces four kinds of color light from source light and forms a projection image by using the four kinds of color light.
2. Description of Related Art
Although color images of a projector are generally produced by using three kinds of primary color light; i.e., red light (R), green light (G), and blue light (B), unfortunately, as shown in the “RELATED ART” in FIG. 7, the above method cannot sufficiently cover a human-visible color gamut. Expansion of a color gamut of the projector is essential in order to faithfully reproduce real and natural colors, and if the projector can independently modulate color light having a wavelength of about 510 nm in addition to the related art red light (R), green light (G), and blue light (B), the expressible color gamut of the projector can be drastically expanded. With this background, projectors which produce color images by using four or more kinds of color light including the three kinds of primary color light have been studied. For example, see Japanese Unexamined Patent Application Publication No. 8-304739 (FIG. 8) and Yamaguchi: “Multi-Primary Color Display”, Proceedings, Color Forum Japan '99, Kougaku Yon Gakkai (Four Optical Related Societies of Japan), pp. 73-79, November 1999.
The projectors of some types using multiple kinds of color light as mentioned above have been devised, for example, as presented in Yamaguchi. Related art projectors of typical types using four kinds of color light will be explained as below.
(1) Surface-dividing-type projectors having a structure in which, as similar to, for example, a triple-panel-type projector equipped with dichroic mirrors arranged in parallel so as to serve as a color-synthesis optical system, color-separation and color-synthesis optical systems are formed by arranging three pairs of dichroic mirrors in parallel, and four electro-optical devices are arranged between the two optical systems. Since a projection image is formed by using the four electro-optical devices to correspond four kinds of color light, a light utilization efficiency of the projector is higher than those of pixel-juxtaposed-type and time-sharing-type projectors, which will be described later, and a high luminance of a projection image can be easily achieved; however, since the projector requires a large number of electro-optical devices and also a large distance between the electro-optical devices and a projection lens in order to synthesize the four kinds of color light with the three dichroic mirrors, it is difficult to reduce the size and the cost of the projector.
(2) Pixel-juxtaposing-type projectors having a structure in which color filters to correspond four colors are arranged on a single plane so as to correspond to respective pixels formed in a pixel array of an electro-optical device, and thus to form a color projection image. Since the projector has a very simple structure and can produce a color projection image with a single electro-optical device, the size and the cost thereof can be easily reduced; however, since four kinds of color light are produced by the color filters, a light utilization efficiency of the projector is very low, whereby it is very difficult to achieve a high luminance of the projection image. Also, since the pixels are juxtaposed so as to correspond to respective spots of color light, high definition of the projection image is unlikely achieved.
(3) Time-sharing-type projectors having a structure in which, as similar to a way of producing a color image of, for example, a single-panel-type projector including a rotary color filter, projection images to correspond four kinds of color light are produced in a time sharing manner by rotating a color filter disk having color filters for four colors, arranged in a sectorial shape, and by displaying them in a temporarily continuous manner so as to impress a human to recognize them as a color image. Since a color projection image can be produced by a single electro-optical device, and also, a multi-color projection image can be easily produced, the size and the cost of the projector can be easily reduced. However, since a display time for each kind of color light is short, a light utilization efficiency of the projector is very low, whereby it is very difficult to achieve a high luminance of the projection image. Also, since the electro-optical device to form an image is required to respond quickly, it has a disadvantage of limited kinds of commercially available electro-optical devices.
(4) Pixel-spatially-disposing-type projectors having a structure in which an electro-optical device having microlenses, each for four pixels, disposed in an arrayed pattern is used, and a plurality of kinds of color light having different output directions from each other are produced from source light by a color-separation optical system formed by four dichroic mirrors arranged in a sectorial shape, hologram elements, or the like, and the plurality of kinds of color light are incident on the corresponding pixels so as to produce a color projection image. Since the color light is produced without a color filter, a light utilization efficiency of the projector is relatively higher than those of the time-sharing-type projector and the pixel-juxtaposing-type projector, and a high luminance of the projection image can be relatively easily achieved. Also, since the color projection image can be formed with a single electro-optical device, the size of the projector is easily reduced; however, since the pixels corresponding to respective spots of color light are juxtaposed in a similar fashion to those in the pixel-juxtaposing-type projector, high definition of the projection image is unlikely achieved. In addition, with collection performed by the microlenses (the maximum collecting angle α0) and directional separation performed by the color-separation optical system (the separation angle β0), each spot of color light separated by the color-separation optical system becomes a diverging ray having a wide angular distribution (the maximum divergent angle α0+β0) and is emitted from the electro-optical device. Although a projection lens having a small F-number and a large diameter greater than a flux diameter of each spot of diverging color light is needed in order to correspond to the diverging ray having a large angular distribution, such a lens is very expensive and the size of the projector is inevitably expanded.
As described above, although realizing a projector using multiple kinds of color light is in theory feasible to a sufficient degree, since it is difficult to achieve a high luminance and high definition of a projection image, to reduce the size and the cost of the projector, and so forth, all at the same time, such a projector of highly practical use has not been achieved.
Accordingly, the present invention provides a compact projector in which, by using four kinds of color light, a projection image is formed so as to expand a color expressible gamut compared to those of the related art projectors, which does not require a large-diameter and expensive projection lens, and which has an excellent light utilization efficiency.